The present invention relates to valves, especially to valves used in connection with a vacuum manifold device for treating liquid samples.
Liquid samples may be treated to test for and/or remove the same or different constituents in the samples, e.g. by solid phase extraction or filtering. In carrying out the treatment, one proposed system, disclosed in U.S. Pat. No. 4,810,471, includes a reagent tube mounted atop a valve and connected to a valve inlet. A long tube connects the valve outlet with a vacuum manifold device disposed therebelow. The sample is introduced into an upper end of the reagent tube, and the valve is opened. Then, a vacuum is applied to the vacuum manifold device to draw the sample through the reagent tube, the valve and the long tube and delivered to a collection container disposed in the vacuum manifold device.
The valve is a low pressure valve comprised of members which are threadedly interconnected such that rotation of one member causes the valve to open or close. The threaded members are formed of plastic, and probably should be machined in order to obtain the necessary dimensional precision.
It would be desirable to provide valve members that can be made by a molding step without any appreciable machining.
Also, it would be desirable to minimize the number of components of the valve. In the above-described U.S. Pat. No. 4,810,471 the valve comprises two threadedly connected parts, a valve seat part disposed between those parts to define a valve seat, and the long tube which is mounted on one of the valve parts.